Do not render rail=abandoned

Per the wiki, railway=abandoned is used for railways where the rails have
been removed. See also the picture on the wiki:
http://wiki.openstreetmap.org/wiki/Tag:railway%3Dabandoned

Such abandoned railways should probably not be rendered on a general purpose
map.

This resolves #3332 on trac.
Merge pull request #542 from math1985/abandoned

Do not render rail=abandoned